Hydraulic vane pumps are used to pump hydraulic fluid in many different types of machines for different purposes. Such machines include, for instance, earth moving, industrial and agricultural machines, waste collection vehicles, fishing trawlers, cranes, and vehicle power steering systems.
Hydraulic vane pumps typically have a housing with a chamber formed therein. A rotor is rotatably mounted in the housing. The rotor is typically of generally cylindrical shape and the chamber has a shape such that one or more rise and fall regions are formed between the walls of the rotor and the walls of the chamber. In the rise regions, a relatively large space opens between the outer wall of the rotor and the inner wall of the chamber. On the leading side of the rise region, there exists a region which is substantially a dwell, although in usual practice there exists a small amount of fall. This is sometimes called a major dwell or major dwell region. The major dwell is followed by a fall region, in which the space between the rotor and the chamber decreases. Outside of the rise, fall and major dwell regions, the space between the outer wall of the rotor and the inner wall of the chamber is small. In practice, this is usually a true dwell of zero vane extension and is sometimes called the minor dwell. The rotor normally has a number of slots and movable vanes are mounted in the slots. As the rotor rotates, centrifugal forces cause the vanes to move to an extended position as they pass through the rise regions. As the vanes travel along the fall regions, the vanes are forced to move to a retracted position by virtue of the rotors contacting the inner wall of the chamber as they move into the region of restricted clearance between the rotor and chamber. Hydraulic fluid lubricates the vanes and the inner wall of the chamber.
Hydraulic vane pumps are usually coupled to a drive, such as to a rotating output shaft of a motor or an engine and, in the absence of expensive space invasive clutches or other disconnecting means, continue to pump hydraulic fluid as long as the motor or engine continues to operate. A rotor of the pump also usually has a rotational speed determined by the rotational speed of the motor or engine.
A problem with known hydraulic vane pumps is that they continuously pump hydraulic fluid, regardless of whether or not a hydraulic system of a machine is being utilised in a working mode of the machine. That is, a machine may be idle or may be in the process of being driven from one job location to another (i.e. in a non-working mode), yet the pump may continue to consume energy in pumping fluid excessively or unnecessarily.
A related problem is that hydraulic hoses, pipes and valves of hydraulic systems of machines such as waste collectors and hydraulic cranes tend to be larger than actually required in order for the machines to carry out lifting in their working mode. That is, lifting may be normally carried out at moderate engine speeds, yet the machines may attain high engine speeds when being driven from one location to another. Consequently, larger and more expensive hydraulic hoses, pipes and valves are required in order to accommodate the higher fluid pressures generated by the pump at high engine speeds.
A problem with some known hydraulic vane motors is that, like with hydraulic vane pumps, in the absence of expensive space invasive clutches or other disconnecting means, hydraulic vane motors may also be worked by the hydraulic fluid incessantly and excessively.
U.S. Pat. No 3,421,413 to Adams et al describes a sliding vane pump in which hydraulic pressure is applied to each vane in order to maintain the vanes in optimum engagement with a cam surface that encircles the rotor which carries the vanes. This patent is directed towards ensuring that the vanes remain in optimum contact with the encircling cam.
U.S. Pat. No. 3,586,466 to Erickson describes a rotary hydraulic motor having a slotted rotor and a movable vane located in each slot. The rotor is journalled in a chamber that defines three circumferentially spaced crescent-shaped pressure chamber sections. The hydraulic motor includes a valve control means and associated passages to be able to selectively control the flow of pressurised fluid to the pressure chamber sections. This allows pressurised fluid to be supplied to one, two or all three pressure chamber sections. When pressurised fluid is delivered to all three pressure chamber sections, low speed, high torque operation occurs. When pressurised fluid is delivered to two pressure chamber sections, higher speed but lower torque operation occurs. When pressurised fluid is delivered to only one pressure chamber section, even higher speed but lower torque operation of the motor occurs.
The hydraulic motor of Erickson also includes an arrangement of passages that allow pressurised fluid to impart radially outward movement to the vanes adjacent the inlet passages to the pressurized chamber sections and to impart radially inward movement to the vanes adjacent the outlet passages of the pressurized chamber sections. Thus, each vane is fluid pressure urged radially outwardly into sealing engagement with the concavity or concave surface of each pressurized chamber section during initial movement of the vane circumferentially across the pressurize chamber section, the vane being moved radially inwardly by fluid pressure at the circumferentially opposite end of the pressurized chamber section, to reduce the frictional load between each vane and the inner peripheral surface portions of the chamber at areas wherein there is little or no circumferential pressure applied to the vanes (see column 4, lines 55 to 72).
The entire contents of U.S. Pat. Nos. 3,421,413 and 3,586,466 are expressly incorporated herein by cross reference.